In the processing of semiconductor devices, such as transistors, diodes, and integrated circuits, a plurality of such devices are typically fabricated simultaneously on a thin slice of semiconductor material, termed a substrate, wafer, or workpiece. In one example of a semiconductor processing step during manufacture of such semiconductor devices, the wafer or other workpiece is typically transported into a reaction chamber in which a thin film, or layer, of a material is deposited on an exposed surface of the wafer. Once the desired thickness of the layer of semiconductor material has been deposited the surface of the wafer, the wafer may be further processed within the reaction chamber, transported out of the reaction chamber for packaging, or transported out of the reaction chamber for further processing.
Known methods of depositing a film of a semiconductor material onto a surface of a wafer include, but are not limited to: (atmospheric and low-pressure) vapor deposition, sputtering, spray-and-anneal, and atomic layer deposition. Chemical Vapor Deposition (“CVD”), one process for fabricating semiconductor devices, is the formation of a stable compound on a heated wafer, or substrate, by the thermal reaction or decomposition of certain gaseous compounds within a reaction chamber. Epitaxial growth is a highly specific type of CVD that requires that the crystal structure of the substrate or wafer be continued through the deposited layer. The reaction chamber provides a controlled environment for safe deposition of stable compounds onto the substrate.
A reaction chamber may be formed of quartz, stainless steel, aluminum, or any other material sufficient to be substantially non-reactive with respect to the reactant gases introduced therein. One commercial epitaxial deposition reaction chamber includes a horizontal flow system in which wafers are placed horizontally on a susceptor and reactant gases flow horizontally in one end of the reaction chamber, across the wafer(s), and out the other end of the chamber. Two types of reaction chambers typically used in CVD processes are cold-wall reaction chambers and hot-wall reaction chambers. Cold-wall reaction chambers are formed of materials in which the walls of the reaction chamber are maintained at a reduced temperature relative to the substrate being processed, for example by actively cooling the reaction chamber walls. Heating the wafer in a cold-wall CVD system is typically accomplished through the use of radiant heat of wavelengths absorbed by the substrate or substrate holder, but the walls of the reaction chamber are largely transparent to the radiant energy wavelengths. Other heating mechanisms can also be used. Hot-wall reaction chambers are formed of materials in which the walls of the chamber are heated while the wafer being processed is simultaneously heated. The walls of the hot-wall reaction chamber are typically closer to the temperature of the substrate being processed relative to the temperature difference in cold-wall reaction chambers.
The reaction chamber used in horizontal CVD systems generally includes at least one inlet port that introduces reactant gases into the reaction chamber and a single outlet port for removal of the reactant gases and by-products that result from chemical reactions between the reactant gases and the exposed surface of the wafer being processed. The reactant gases typically contain chemicals or compounds for providing a material deposition on the wafer in the form of a thin film layer. The reactant gases may also include chemicals or compounds for removing, or etching, a portion of the surface of the bare wafer or a portion of the surface of a deposited thin film, such as in selective deposition processes.
During deposition of a thin film layer on the surface of the wafer, the exhaust, or by-products, from the chemical reaction and any excess reactant gases that were previously introduced into the reaction chamber are continually removed therefrom. The exhaust and excess reactant gases are typically withdrawn from the reaction chamber by way of the outlet port. The excess reactant gases and the exhaust from the chemical reaction can be removed from the reaction chamber as a result of a pressure differential caused by the reactant gases being input into the reaction temperature at a pressure greater than the pressure downstream from the reaction chamber. In the alternative, a vacuum can be operatively connected to the outlet port, whereby the exhaust and excess reactant gases are withdrawn from the reaction chamber by a suction force.
With conventional reaction chambers, the flow pattern within the reaction chamber may develop turbulence along the walls or corners of the reaction chamber. The flow turbulence can reduce or eliminate the amount of reactant gases at localized areas within the reaction chamber, which is particularly problematic in the areas adjacent to, or above, the exposed surface of the workpiece being processed. The turbulence of the reactant gases may cause a reduced amount of reactant gases flowing across portions of the wafer within the reaction chamber. Non-laminar flow and laminar flow may both create areas or regions of a reduced amount of reactant gases flowing across portions of the wafer within the reaction chamber. Any type of flow of reactant gases within the reaction chamber that would cause reduced or lack of reactant gases flowing across areas of a wafer reduce the likelihood of an even deposition across the entire surface of the wafer. Recirculation caused by turbulence can affect not only the uniformity of the deposition but can also create contamination problems.